Learn Croatian: Imam samo deset minuta. - I have only ten minutes.

In Croatian, when you use a number from five onwards (like deset), the noun that follows must be in the genitive plural case. For the feminine noun minuta, the genitive plural is also minuta. It looks exactly like the singular form, but it is actually plural here! For comparison, if you had two, three, or four minutes, you would use minute.

Where is the word for "I" in this sentence?

It is hidden in the verb! The verb imam (I have) ends in -m, which already tells us the subject is "I". In Croatian, you usually drop the pronoun ja unless you want to add special emphasis.

Could I put the word samo at the very end of the sentence?

It is best to keep it where it is. The adverb samo (only) almost always goes directly before the word or phrase it is modifying. Since it modifies deset minuta (ten minutes), it needs to sit right in front of that phrase.